Low formaldehyde, high gel fraction latex binder

ABSTRACT

A low formaldehyde, high gel fraction latex binder is made utilizing a compound having the formula ##STR1## wherein R and R&#39;, independently, is an alkyl having from 1 to 10 carbon atoms, and R 4  is hydrogen, or wherein R 3  and R 4 , independently is an alkyl, an aromatic, or combinations thereof having from 1 to 10 carbon atoms, or wherein said R 3  and R 4  are connected to form an internal amide, and wherein the isopropenyl group is either in the ortho, meta or para position. The latex binder is generally an emulsion or latex copolymer made from various monomers including at least one or more conjugated dienes having a total of from 4 to 10 carbon atoms with butadiene being preferred and from one or more vinyl-substituted aromatics having from 8 to 14 carbon atoms, with styrene being preferred. The amount of the above formulation compounds is generally from about 0.25 to about 20 parts by weight based upon 100 parts by weight of the one or more conjugated dienes and the vinyl-substituted aromatic monomers. The latex binder has good stability, and has many applications such as to bind a paper-coating composition to a cellulose substrate, or to bind non-woven fibers together. The latex binder generally contains 10 parts or less by weight of formaldehyde per million parts by weight and desirably contains nil, that is, no detectable amounts of formaldehyde therein, even after extended periods of time, e.g., 28 days.

CROSS-REFERENCE

This is a division of application Ser. No. 08/122,821, filed Sep. 16,1993 now U.S. Pat. No. 5,326,853, of Peter Charles Hayes, for "LOWFORMALDEHYDE, HIGH GEL FRACTION LATEX BINDER."

FIELD OF THE INVENTION

This invention relates to high gel fraction polymeric latex compositionswhich can be utilized for paper coating compositions, for bindingnon-woven fibers together, and for processes for making and using thesame. More particularly, the invention relates to such high gel fractionpolymeric latex binder compositions wherein formaldehyde generation issubstantially eliminated.

BACKGROUND OF THE INVENTION

Latex binder compositions have been used in a wide variety ofapplications such as adhering paper coatings to cellulosic substrates,in carpet and rug backings, and in various non-woven products which havegained broad acceptance as replacements for woven fabrics, includingsuch articles as facings or top sheets in diapers, incontinence pads,sanitary napkins, hospital gowns, and other single and multiple-usenon-woven products.

Conventional latex binders have generally been prepared from acrylicpolymers, styrene/acrylate copolymers, or styrene/butadiene copolymerscontaining N-methylol functionality which, upon curing, generatesubstantial quantities of formaldehyde, typically from 200 to 500 ppm ormore. It is desirable to use binders which are essentially free offormaldehyde generation. Formaldehyde-free latex binders include variousurethane polymers, acrylic polymers, styrene/acrylate copolymers, andthe like, such as those disclosed in U.S. Pat. Nos. 2,837,462;4,207,367; 4,381,332; 5,030,507, and others. However, none of the priorart discloses a suitable conjugated diene/vinyl-substituted aromaticcopolymer latex binder which is free of formaldehyde formation, andwhich also exhibits superior coagulation stability and mechanicalstability while imparting excellent wet tensile strength to cellulosicarticles such as paper.

SUMMARY OF THE INVENTION

It has been discovered that high gel fraction latex binder compositionsmade from one or more conjugated diene monomers, one or morevinyl-substituted aromatic monomers, a ketoxime or amide blockedisopropenyl-α-α-dimethyl benzyl isocyanate, and one or more monomerscontaining functional groups such as hydroxyl, carboxyl, or primary orsecondary amides can be prepared without generating significantquantities of formaldehyde. It has been further discovered that theforegoing binder compositions, described in greater detail hereinafter,unexpectedly exhibits superior coagulation as well as mechanicalstability and impart superior wet tensile strength when applied tocellulosic articles.

The polymeric latex binder compositions of the invention can optionallybe made from one or more ester monomers, vinyl chloride or vinylidenechloride monomers, and various stabilizer monomers.

The above monomers containing low amounts of conjugated diene, i.e. lessthan 60 percent by weight, are polymerized under acidic conditions andhigh temperatures and achieve high conversion levels of at least 90percent to form a high gel fraction (e.g. at least 70 percent) latexbinder which upon application to a substrate can be cured, i.e.crosslinked, upon heating.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 relates to a cross-sectional view of a paper coating bound to acellulose substrate with the latex binder of the present invention.

FIG. 2 relates to a cross-sectional view of nonwoven fibers bound to oneanother with the latex binder of the present invention.

DETAILED DESCRIPTION

The binder-forming monomers of the present invention forming theemulsion or latex binder composition (i.e., an aqueous suspension of acopolymer) are generally well known to the art and to the literature andinclude a primary, sizeable or main amount of at least a conjugateddiene monomer and a vinyl-substituted aromatic monomer, as well assmaller amounts of various functional containing monomers. Optionalmonomers include various esters, vinyl chloride or vinylidene chloride,acrylonitrile, and the like. The conjugated diene monomers generallycontain from about 4 to 8 carbon atoms, and desirably from 4 to 6 carbonatoms. Examples of specific diene monomers include piperylene, isoprene,2,3-dimethyl-1,3-butadiene, and preferably 1,3-butadiene. Mixtures oftwo or more conjugated dienes can also be utilized. Thevinyl-substituted aromatic monomers which can be utilized in associationwith the conjugated dienes to form copolymers generally have from 8 toabout 12 carbon atoms. Specific examples include α-methyl styrene,p-tertiary butyl styrene, methyl vinyl toluene, p-vinyl toluene, 3-ethylstyrene, and the like, with styrene being preferred. Mixtures of two ormore vinyl-substituted aromatic monomers can also be utilized. Theamount of the one or more conjugated diene monomers which can beutilized is generally small in comparison to latexes utilized for tires,generally ranging from about 10 to about 90 percent based upon the totalamount by weight of the conjugated diene monomers and thevinyl-substituted aromatic monomers. With regard to non-wovenapplications, the desired range is from about 25 to about 55 or 60percent and preferably from about 30 to about 50 percent by weight. Theamount of vinyl-substituted aromatic monomers is generally thedifference, that is, from about 10 to about 90 percent by weight, andwith regard to non-woven applications from about 40 or 45 percent toabout 75 percent by weight, and preferably from about 50 to about 70percent by weight. With regard to cellulose applications, the desiredamount of conjugated diene monomers is from about 15 to about 50 percentby weight and preferably from about 25 to about 40 percent by weight.The amount of the vinyl-substituted aromatic monomers for celluloseapplications is generally the difference, that is generally from about50 percent to about 85 percent and preferably from about 60 percent toabout 75 percent by weight based upon the total weight ofvinyl-substituted aromatic and conjugated diene monomers.

Examples of monomers containing functional groups include variousunsaturated acids and various unsaturated amides or derivatives thereofhaving a total of from about 3 to about 12 carbon atoms with theexception of N-methylol-functional ethylenically unsaturated monomers.Acid monomers are desired since they improve colloidal stability as wellas adhesion to a substrate. The amount of such monomers is generallyfrom about 0.1 to about 15 parts by weight, desirably from about 0.5 toabout 10 parts, and preferably from about 1.0 to about 5.0 parts byweight for every 100 parts by weight of the one or more conjugated dieneand vinyl-substituted aromatic monomers. Examples of such suitablemonomers include acrylic acid (preferred), methacrylic acid, maleicacid, fumaric acid, itaconic acid (preferred), hydroxyethyl acrylate (apreferred compound), hydroxyethyl methacrylate, hydroxymethyl acrylate,hydroxymethyl methacrylate, hydroxypropyl acrylate, hydroxypropylmethacrylate, (meth) acrylamide (preferred), dimethylacrylamide,derivatives of the various amide containing monomers, and combinationsof the foregoing.

The present invention does not utilize and hence is free fromN-methylol-functional ethylenically unsaturated monomers includingN-methylolamides of ethylenically unsaturated carboxylic acids having3-10 carbons, such as N-methylolacrylamide, N-methylolmethacrylamide,N-methylolmaleimide, N-methylolmaleinamic acid, N-methylolmaleinamicacid esters, N-methylolamides of the vinyl aromatic acids such asN-methylol-p-vinylbenzamide, and the like. Also essentially excluded orabsent from the present latex-forming monomers are mixtures of variousN-methylol-functional monomers such as mixtures of N-methylolacrylamideand acrylamide and mixtures of N-methylolmethacrylamide andmethacrylamide. If any of such compounds are utilized, the amount isvery minute, such as 0.1 part or less and desirably 0.05 parts or lessby weight based upon 100 parts by weight of the total monomers, oreffective amounts which yield generally 10 parts or less per million anddesirably 5 parts or less, or 3 parts or less, or even 2 parts or lessof formaldehyde per million of latex binder.

The binders of the present invention are thus essentially free of anychemical functional group (e.g. OH, NH₂, COOH) crosslinks, althoughperhaps contain very minor inherent crosslinking obtained by thereaction of the various unsaturated, non-functional groups (i.e. solelyhydrocarbon) such as those in divinyl benzene. The chemical crosslinkingwhich does occur to form the high-gel content of the latex bindercomposition is thought generally to occur through the remainingunsaturated groups of the reacted butadiene monomers. Should the gelcontent not be high enough, monomers generating nonfunctional crosslinkstructures can be utilized such as divinyl benzene discussed more fullyhereinbelow.

Optional esters which are often utilized to improve ink gloss coatingproperties in paper applications include the various alkyl(meth)acrylate and hydroxyl derivatives thereof, wherein the alkylportion has from 1 to 10, preferably from 1 to 4 carbon atoms withspecific examples including butyl acrylate, 2-ethylhexyl acrylate,propyl acrylate, ethyl acrylate, and the like. The amount of such estermonomers is generally from about 0.1 to about 10 parts by weight, andpreferably from about 1.0 to about 5 parts by weight for every 100 partsby weight of the one or more vinyl substituted aromatic and conjugateddiene monomers.

Optionally, vinyl chloride and vinylidene chloride monomers orcombinations thereof can be utilized in amounts from about 0.1 up toabout 35 parts by weight and preferably from about 5 percent to about 20parts by weight for every 100 parts by weight of the one or morevinyl-substituted aromatic and conjugated diene monomers.

Another optional monomer is acrylonitrile which can be utilized in anamount of from about 0.1 to about 25 and desirably from about 5 to about15 parts by weight for every 100 parts by weight of the one or morevinyl-substituted aromatic and conjugated diene monomers.

Other conventional monomers can optionally be utilized in conventionalamounts such as various organic salts, for example sodium styrenesulfonate or the 3-sulfopropyl(meth)acrylate salt of sodium or potassiumto control particle size.

The above monomers are polymerized in the presence of water to form thelatex binder of the present invention in accordance with conventionalemulsion polymerization procedures and techniques. In addition to thesemonomers, free-radical initiators, optional chain transfer agents,various emulsifiers (such as anionic surfactants), chelating agents, andthe like can be utilized as set forth in U.S. Pat. No. 5,166,259, toSchmeing and White, which is hereby fully incorporated by reference.

The free-radical initiators utilized to polymerize the various abovelatex binder-forming monomers include sodium persulfate, ammoniumpersulfate, potassium persulfate, and the like. Other free-radicalinitiators can be utilized which decompose or become active at thetemperature utilized during polymerization such as various peroxides,e.g., cumene hydroperoxide, dibenzoyl peroxide, diacetyl peroxide,dodecanoyl peroxide, di-t-butyl peroxide, dilauryl peroxide,bis(p-methoxy benzoyl) peroxide, t-butyl peroxy pivalate, dicumylperoxide, isopropyl percarbonate, di-sec-butyl peroxidicarbonate;various azo initiators such as azobisdimethylvaleronitrile,2,2'-azobisisobutyronitrile, 2,2'-azobis(2-amidinopropane)dihydrochloride, 2,2'-azobis-2-methyl-butyronitrile,2,2'-azobis(methylisobutyrate), and the like, and mixtures thereof. Theamount of the free-radical initiators is generally from about 0.25 toabout 2.0, and preferably from about 0.5 to about 1.5 parts by weightfor every 100 parts by weight of the total monomers.

Optional chain transfer agents include mercaptans such as the alkyland/or aryl mercaptans having from 8 to about 18 carbon atoms andpreferably from about 12 to about 14 carbon atoms. The tertiary alkylmercaptans having from 12 to 14 carbon atoms are highly preferred.Examples of suitable mercaptans include n-octyl mercaptan, n-dodecylmercaptan, t-octyl mercaptan, t-dodecyl mercaptan, tridecyl mercaptan,tetradecyl mercaptan, hexadecyl mercaptan, and the like, as well asmixtures thereof. The amount of the chain transfer agent utilized isgenerally from about 0.01 to about 5 parts by weight and desirably fromabout 0.1 to about 1.0 part by weight for every 100 parts by weight ofthe total monomers.

The emulsifiers can generally be any surfactant, soap, or the like,which are well known to the art and to the literature and stable at thepH of the present latexes, that is, from about 1.5 to about 7.0, andinclude the various alkyl sulfates, the various alkyl sulfosuccinates,the various alkyl aryl sulfonates, the various α-olefin sulfonates, thevarious quaternary ammonium salts, the various amine salts, nonyl oroctyl phenol reaction products of ethylene oxide and the like. The alkylportion of the various emulsifiers generally has from 8 to 18 carbonatoms. Examples of suitable surfactants which desirably are anionicinclude sodium lauryl sulfate, various sodium sulfosuccinates such assodium dimethylamyl sulfosuccinate, e.g., Aerosol MA80, disodium dodecyldiphenyl oxide disulfonate (Dowfax 2A1), sodium dicyclohexylsulfosuccinate, Aerosol A-196, and the like. Naturally, an amount of anemulsifier is utilized to obtain an aqueous emulsion of the variousmonomers. Such an amount is typically from about 0.5 to about 5 or 6parts by weight for every 100 parts by weight of the monomers. Othersurfactants can be utilized such as those set forth in Surface ActiveAgents, Schwartz and Perry, Vol. I, Interscience Publishers, Inc., NewYork, 1958; Surface Activity, Moilliet, Collie and Black, D. VanNostrand Company, Inc., New York, 1961; Organic Chemistry, Fieser andFieser, D.C. Heath and Company, Boston, 1944; and The Merck Index,Seventh Edition, Merck & Co., Inc., Rahway, NJ, 1960, all of which arehereby fully incorporated by reference.

Chelating agents can be utilized during polymerization to tie up variousmetal impurities as well as to achieve a uniform polymerization. Theamounts of such chelating agents is generally small, such as from about0.01 to about 0.25 parts by weight for every 100 parts by weight of thetotal weight of the monomers. Examples of suitable chelating agentsinclude ethylene diamine tetraacetic acid, nitrilotriacetic acid, citricacid, and their ammonium, potassium, and sodium salts.

Monomers capable of generating non-functional crosslinked structuresduring the polymerization of the various monomers and thereby contributeto the creation of a high gel fraction latex are optionally incorporatedin amounts of from about 0.5 to about 5 parts by weight, desirably fromabout 0.1 to about 2 parts by weight and preferably from about 0.1 toabout 1 part by weight per 100 parts by weight of the conjugated dieneand vinyl substituted aromatic monomers. Examples of such compoundsinclude divinyl benzene, ethylene glycol dimethacrylate, di(isopropenyl)benzene, and the like.

An important aspect of the present invention is the utilization of aketoxime or amide blocked isopropenyl α,α-dimethyl benzylisocyanate(TMI) compound having the formula ##STR2## wherein R and R',independently, is an alkyl containing from 1 to about 10 carbon atoms,more desirably from 1 to about 4 carbon atoms, and more preferably 1 or2 carbon atoms with the ketoxime blocking group, being e.g. acetoneoxime, methyl ethyl ketoxime, methyl isobutyl ketoxime, methyl amylketoxime, and the like, with methyl ethyl ketoxime being preferred.

Other suitable blocking agents include various primary or secondaryamide compounds, wherein R⁴ is hydrogen, or wherein R³ and R⁴,independently, is an alkyl, an aryl, or combinations thereof, havingfrom 1 to 10 carbon atoms with 2 to 5 being preferred and wherein R³ canbe connected to R⁴ to form an internal, i.e. cyclic, amide. Examples ofsuitable amides include caprolactam, pyrrolidone, acetamide, butyramide,benzylamide, and the like.

In either formulation, the isopropenyl group is in either the meta,ortho, or para position with the meta position being preferred.

The amount of the ketoxime-blocked or amideblocked TMI utilized in thepresent invention is generally from about 0.25 to about 20 parts;desirably from about 0.5 to about 5.0 parts; and preferably from about0.5 to about 2.5 parts by weight per 100 parts by weight of theconjugated diene and the vinyl-substituted aromatic monomers.

The various latex-forming monomers of the present invention arepolymerized by free radicals according to any conventional methodincluding batch, incremental, or continuous, in the presence of aneffective amount of water to enable the formation of an emulsion as wellas proper mixing of the various additives, heat transfer, and the like.Polymerization is generally carried out from about 50° C. to about 90°C., and desirably from about 65° C. to about 75° C. Polymerization isgenerally conducted in an acidic medium when acidic monomers areutilized and the pH of the latex binder is generally from about 1.0 toabout 6.5, desirably from about 1.5 to about 4.0, and preferably fromabout 1.5 to about 3.0 being preferred. Such high polymerizationtemperatures result in high conversion levels of monomer to copolymersuch as at least 90 percent, desirably at least 95 or 98 percent andpreferably at least 99 percent. Such latex polymers also contain highgel fractions. That is, generally at least 70 percent by weight to about95 or 97 percent by weight, desirably at least 80 percent by weight andpreferably at least 90 percent by weight, that is of insoluble weightpercent fraction in toluene at 20° C. The amount of solids, that is, thecopolymer or binder, is generally from about 35 to about 60, andpreferably from about 40 to about 50 percent by weight based upon thetotal weight of the binder and the remaining ingredients, for example,water. The average particle size of the binders after filtering isgenerally from about 1,000 to about 3,000 Å and desirably from about1,200 to about 1,500 Å.

An important advantage of the latex binder composition is that it, aswell as the binder per se, have very low amounts of aldehyde therein andgenerally are aldehyde-free. That is, the amount of aldehyde, e.g.,formaldehyde, is generally 10 parts or less, desirably 5 parts, 3 parts,or 2 parts or less, and preferably 1 part or 0.7 part or less permillion parts by weight of the latex binder composition. Accordingly,the amount of aldehyde in the binder per se is the same as the rangesset forth above, e.g., 10 parts or less by weight based upon one millionparts by weight of binder. Another unexpected advantage is that thelatex binders have good storage stability in that the aldehyde contentthereof essentially remains the same after one day, one week, two weeks,three weeks, and even four weeks. For example, after 28 days, the amountof aldehyde in the latex binder composition is still appreciably thesame, i.e., within 5 or 7 percent of the original or initial aldehydecontent.

The latex binder also has good coagulation stability. Thus, very lowlevels of coagulant, especially fine-size coagulant such as thatretained on 325 Tyler mesh, exist after filtering of the latex, that is,0.1 percent or less, desirably 0.05 percent or less, more desirably 0.02percent or less, and preferably 0.01 percent or less by weight basedupon the total weight of the latex solids. Low levels of coagulant existeven after extended periods of time, for example, three months, sixmonths, and even nine months. At six months, the amount of coagulantretained on 325 Tyler mesh, after filtering the latex, is generally 0.05percent or less, desirably 0.02 percent or less, and preferably 0.01 orless by weight based upon the total weight of the latex solids.

The latex binder of the present invention has many applications and canbe utilized on cellulosic nonwoven materials such as paper, e.g., offsetprinting paper, towels, various paper tapes, paper containers, and thelike, and is particularly well suited for industrial wipes and toweling.When utilized as a paper coating, the binder generally comprises about10 percent by weight of the paper coating formulation with a greatmajority of the same being comprised of clay, and the like, whereby thebinder serves to bind the clay to the paper surface. The latex bindercan also be applied to other non-woven substrates such as non-wovenfibers, e.g., polyester, polypropylene, rayon, or nylon, or combinationsof cellulosic and synthetic fibers, to non-woven textiles such as mats,to carpet backings, to various disposable products for use in themedical industry such as face masks, gowns, gloves, and the like.

Although the high gel fraction binders of the present invention aregenerally highly crosslinked, application of the same to a substrate,and the like, resulting in the formation of a laminate, etc., and thesubsequent application of heat results in deblocking of the ketoxime- oramide-blocked TMI with further crosslinking. The same results in theimprovement of various properties such as wet tear strength of thecomposite or laminate, improved bond strength between various fibers orlaminates, and the like. The cure temperature with regard to theapplication of the binder to a non-woven, non-cellulosic substrate isgenerally from about 100° C. to about 170° C. whereas the curetemperature with respect to cellulose or paper substrates is generallyfrom about 70° to about 100° C. During cure, the generated freeisocyanate groups generally react with functional groups such as amideor hydroxyl located in other polymers thereby crosslinking the same,with hydroxyl groups as contained in the cellulose substrate, andthereby form chemical bonds yielding good adhesion, improved wet tensilestrength, wet rub, and the like.

A specific use of the latex binder of the present invention is to bind apaper coating composition to a cellulose substrate as shown in FIG. 1wherein the cellulose is generally indicated by the number 10. The papercoating composition 12 is known to the art and to the literature andgenerally includes various fillers such as high brightness claypigments, calcium carbonate, titanium dioxide, small amounts of sodiumhydroxide to control the pH, small amounts of calcium stearate to act asa lubricant, water, sodium polyacrylic acid to act as a dispersant forthe clay, starch, for example, oxidized starch, protein binders such assoybean protein, polyvinyl alcohol binders, and the like. From about 4to about 25 parts by weight and desirably from about 5 to about 20 partsby weight of the latex binder solids, i.e., dry binder, per 100 parts offiller (e.g., clay, calcium carbonate, titanium dioxide, etc.) isgenerally utilized and the same are mixed along with the above-notedother paper coating additives in any conventional mixer, e.g., a Cowlesblade mixer or a ball mill. The paper-coating composition containing asmall amount of the latex binder of the present invention is then coatedon a paper substrate as by using an air knife coater, a blade coater, ora roll coater. The substrate is then dried in a conventional hot-airoven and/or infrared drying oven. The paper is then generallysuper-calendered at elevated temperatures as from about 70° C. to about100° C., and at high pressure whereby cure of the binder 15 occursbinding the paper coating composition to the cellulose substrate. Thecoating or laminate thus produced has improved wet tear strength.

The high gel fraction latex binder 15 of the present invention can beapplied to non-woven fibers 20 such as polyester, cellulosic, ormixtures of cellulosic and synthetic fibers to bind the same together,see FIG. 2. The binder can be applied to the fibers in any conventionalmanner as by spraying an approximately 20 percent solid latex solution,and the like. Upon heating the high gel fraction binder to curetemperatures of approximately 100° to about 170° C., the TMI becomesunblocked and reacts in a manner as set forth above thereby binding thevarious fibers or strands together.

The invention will be better understood by reference to the followingexamples which serve to illustrate the invention, but not to limit thesame.

Apparatus

A one-gallon, stainless steel pressure reactor equipped with monomeraddition ports, stirrer, and temperature and pressure measurementdevices was used. Cooling was provided by an external water bath.

EXAMPLE 1

A mixture of deionized water 1045 g, Dowfax 2A1 (15 percent) 25 g,itaconic acid 22 g, Aerosol A196 (10 percent) 105 g, EDTA solution (40percent) 4 g and styrene 112 g were stirred and heated to 65° C. (undernitrogen). A solution of sodium persulfate 7.5 g in deionized water 142g was then added to the reactor. After 30 minutes the monomer andaqueous streams as set forth in Table I were added to the reactor at 60°C. over a period of 6 hours.

                  TABLE I                                                         ______________________________________                                        AQUEOUS STREAM   MONOMER STREAM                                               ______________________________________                                        DI water 320 g   Styrene 576 g                                                Dowfax 2A1 (15%) 60 g                                                                          Butadiene 690 g                                                               Acrylamide (50%) 60 g                                                         Divinyl Benzene (55%)                                                         6.25 g                                                                        Hydroxyethyl Acrylate 30 g                                                    TMI/MEKO 30 g                                                                 Dodecyl mercaptan 3.75 g                                     ______________________________________                                    

After 6 hours the temperature was raised to 71° C. and the reactioncontinued for 3 hours (total solids approximately 44 percent). The pH ofthe high gel fraction latex binder was 2.1 and the amount of gel at 20°C. in toluene was 90 percent. The conversion of monomers to polymer wasat least 99 percent.

Post-Addition re Storage and Stability

The following was added to the reactor and then the latex wassteam-stripped and filtered in a conventional manner.

Dowfax 2A1 (15 percent) 20 g, D.I. water 85 g, 28% ammonia 25 gDREW L198 antifoam 4 g Proxel GXL (25%) biocide 8 g, Bostex 490B (35%)antioxidant 20 g.

    ______________________________________                                        Properties                                                                    ______________________________________                                        Total solids content:                                                                              44.2 percent                                             pH:                  7.3                                                      Surface tension:     40 dynes/cm                                              Brookfield viscosity:                                                                              50 cps                                                   Particle size:       approx 1450 Å                                        Coagulation collected                                                                              3.0 grams                                                on 325 Tyler mesh:                                                            ______________________________________                                    

The above binder made in accordance with the present invention containedless than 0.7 part by weight of formaldehyde per million parts by weightof the latex binder. The amount of formaldehyde after 28 days of agingwas also less than 0.7 parts per million.

EXAMPLE 2

A conventional latex binder composition control (Latex 1 of Table II)was prepared in a manner similar to Example I as were latexes A, B and Cof the present invention. The amounts indicated are in weight units,i.e., control contained 46 parts by weight styrene, 50 parts by weightbutadiene, 2 parts by weight acrylic acid, 1.5 parts by weight itaconicacid and 0.5 parts by weight divinyl benzene.

                                      TABLE II                                    __________________________________________________________________________                                           AVERAGE                                                                       SOLVENT                                                              WET TENSILE                                                                            TENSILE,                                                                             FORMALDE-                       LATEX                                                                              COMPOSITION           Y.I.                                                                             LBS.     LBS.   HYDE PPM                        __________________________________________________________________________    Control                                                                            STY/BD/AA/IA/DVB      8.4                                                                              17.7     16.1   10                                   46/50/2.0/1.5/0.5                                                        A    STY/BD/IA/AA/HEA/TMI MEKO/DVB                                                                       7.1                                                                              21.7     29.7   <0.7                                 43.25/48.75/1.5/2.0/2.0/2.0/0.5                                          B    STY/BD/IA/AAD/HEA/TMI MEKO/DVB                                                                      7.3                                                                              23.0     32.0   <0.7                                 46/46/1.5/2.0/2.0/2.0/0.5                                                C    STY/BD/IA/AAD/TMI MEKO/DVB                                                                          7.3                                                                              22.0     25.0   <0.7                                 48/46/1.5/2.0/2.0/0.5                                                    Control                                                                            A commercial styrene-butadiene                                                                      8.1                                                                              22.0     28.0   120                                  copolymer made with 2.5 N-methyl                                              acrylamide and 2.5 acrylamide                                            __________________________________________________________________________     BD = BUTADIENE                                                                YI = YELLOWNESS INDEX                                                         IA = ITACONIC ACID                                                            AAD = ACRYLAMIDE                                                              AA = ACRYLIC ACID                                                             HEA = HYDROXYETHYL ACRYLATE                                                   DVB = DIVINYL BENZENE                                                         TMI MEKO = METHYLETHYLKETOXIME of mTMI                                   

Each of the above latexes were applied to Whatman sheets and dried for 5minutes at 315° F. (158° C.). The amount of latex applied in each casewas 20 percent by weight (45 percent solids) of the total weight of thelatex and paper.

The dried sheets were then tested for yellowness, wet tensile strength(in water), and solvent tensile strength using a variety of differentsolvents such as toluene, heptane, mineral spirits. The solvent tensiletest is an average tensile strength of paper soaked in toluene, heptaneand mineral spirits for a period of 3 hours and tested immediatelythereafter without drying. The results indicate that the latexcompositions of the invention have a lower yellowness index and muchbetter wet tear strength and average solvent tear strength than thefirst control. The second control shows that a conventional or typicalstyrene-butadiene polymer made utilizing N-methylol acrylamide andacrylamide while having good wet tensile strength and average solventtensile properties having exceeding high amounts, that is 120 parts permillion of formaldehyde.

EXAMPLE 3

Two latex binder compositions in accordance with the invention wereprepared in a manner as set forth in Example 1 and had the compositionshown in Table III. The samples were then tested for mechanicalstability by determining the amount of coagulum formed after 30 minutesof shearing in a high speed blender. The data shows that the inclusionof carboxylic acids results in dramatic improvements in coagulationstability. It was also observed that the inclusion of carboxylic acidsin the latex composition provides for better processing in the reactor.

                                      TABLE III                                   __________________________________________________________________________                    REACTOR                                                       LATEX COMPOSITION                                                                             "CLEANLINESS"                                                                           MECHANICAL STABILITY                                __________________________________________________________________________    STY/BD/IA/AA/TMI.MEKO                                                                         Good      16 PPM (0.0016%)                                    48.5/46/1.5/2/2                                                               STY/BD/TMI.MEKO Build up of Poly-                                                                       178,071 PPM (17.81%)                                52/46/2         mer on Walls of                                                               Reactor                                                       __________________________________________________________________________     NOTE:                                                                         IA = Itaconic Acid                                                            AA = Acrylic Acid                                                        

EXAMPLE 4 COMPARATIVE EXAMPLE USING UNBLOCKED TMI MONOMER

When a latex was prepared in a manner similar to Example 1 except thatthe TMI.MEKO and hydroxyethyacylate was omitted and 30 g of TMI monomerwere substituted, the polymer emulsion was very unstable in a colloidalsense and the product flocculated in the reactor was approximately 60percent of the reaction ingredients. The polymer emulsion changed to asolid thick mass which could not be further processed. Thus, physicaltest data could not be obtained.

While in accordance with the Patent Statutes a best mode and preferredembodiment has been presented, the scope of the invention is not limitedthereto, but rather is measured by the scope of the attached claims.

What is claimed is:
 1. In an article comprising a cellulosic substrateand a paper coating composition bound to said substrate by a binder madeby the emulsion polymerization of monomers comprising a primarycomonomer component of one or more conjugated diene monomers having from4 to 8 carbon atoms and one or more vinyl-substituted aromatic monomershaving from 8 to 12 carbon atoms; and from one or more functionalcontaining monomers in an amount of from about 0.1 to about 15 parts byweight per 100 parts by weight of said primary comonomer component,theimprovement comprising the use of from about 15 to 50 percent by weightof said one or more conjugated diene monomers and from about 50 to about85 percent by weight of said one or more vinyl substituted aromaticmonomers, and a blocked crosslinking agent in an amount of from about0.5 to about 20 parts by weight per 100 parts by weight of said primarycomonomer component, said crosslinking agent being one or more ketoximeor amide blocked isopropenyl α,α-dimethyl benzyl isocyanate compoundshaving the formula ##STR3## wherein R and R' independently, is an alkylhaving from 1 to 10 carbon atoms, and R⁴ is hydrogen, or wherein R³ andR⁴, independently is an alkyl, an aromatic, or combinations thereofhaving from 1 to 10 carbon atoms, or wherein said R³ and R⁴ areconnected to form an internal amide.
 2. In a coated cellulose substrateaccording to claim 1, wherein the amount of said conjugated diene isfrom about 25 to about 40 percent by weight and the amount of said vinylsubstituted aromatic is from about 60 to about 75 percent by weight,wherein R and R¹ independently is methyl or ethyl, wherein R³ and R⁴ arejoined together and is caprolactam, wherein the amount of said one ormore ketoxime or amide blocked isopropenyl e, amethyl benzyl isocyanatecompounds is from about 0.5 to about 5.0 parts per 100 parts by weightof said primary comonomer component, and wherein said isopropenyl groupis located in the meta position.
 3. In an article comprising non-wovenfibers bound together by a binder made by the emulsion polymerization ofmonomers comprising a primary comonomer component of at least one ormore conjugated diene monomers having from 4 to 8 carbon atoms and oneor more vinyl-substituted aromatic monomers having from 8 to 12 carbonatoms; and from one or more functional containing monomers in an amountof from about 0.1 to about 15 parts by weight per 100 parts by weight ofsaid primary comonomer component,the improvement comprising the use offrom about 25 to 60 percent by weight of said one or more conjugateddiene monomers and from about 40 to about 75 percent by weight of saidone or more vinyl substituted aromatic monomers, and a blockedcrosslinking agent in an amount of from about 0.5 to about 20 parts byweight per 100 parts by weight of said primary comonomer component, saidcrosslinking agent being one or more ketoxime or amide blockedisopropenyl α,α-dimethyl benzyl isocyanate compounds having the formula##STR4## wherein R and R' independently is an alkyl having from 1 to 10carbon atoms, and R⁴ is hydrogen, or wherein R³ and R⁴, independently,is an alkyl, an aromatic, or combinations thereof having from 1 to 10carbon atoms, or wherein said R³ and R⁴ are connected to form aninternal amide.
 4. In an article according to claim 3, wherein theamount of said conjugated diene is from about 30 to about 50 percent byweight and the amount of said vinyl substituted aromatic is from about50 to about 80 percent by weight, wherein R and R¹ independently ismethyl or ethyl, wherein R³ and R⁴ are joined together and iscaprolactam, wherein the amount of said one or more ketoxime or amideblocked isopropenyl α,α-methyl benzyl isocyanate compounds is from about0.5 to about 5.0 parts per 100 parts by weight of said primary comonomercomponent, and wherein said isopropenyl group is located in the metaposition.